Light-emitting devices such as optical semiconductor devices generally include, for example, LED (light-emitting diode element) or LD (laser diode) that emits blue light, and a phosphor layer that is capable of converting the blue light to yellow light and is provided on the LED. The light-emitting device emits white light by color mixture of blue light emitted from the LED and passed through the phosphor layer with yellow light obtained by converting the wavelength of a portion of the blue light at the phosphor layer.
Patent Document 1 (see Patent Document 1 below) has proposed, for such a phosphor layer, for example, a conversion element composed of a ceramic material.
Patent Document 1 discloses a conversion element having a density of 97% or more of the density of theoretical solid-state ceramic material, and having pores therein with a diameter of substantially 250 nm to 2900 nm.
The conversion element of Patent Document 1 has micropores on the order of nano, and therefore improves transmittance in a wider viewing angle.